The safety and efficacy of current vaccines are reviewed for high-risk populations, such as those with underlying medical conditions or occupational or lifestyle circumstances. The morbidity and mortality from vaccine-preventable diseases are high among persons with underlying medical conditions; thus, influenza and pneumococcal polysaccharide vaccines are recommended for those with cardiac disease, diabetes mellitus, or chronic obstructive pulmonary disease. For the same reasons, influenza vaccine is recommended for pregnant women and for persons with asthma. Health-care workers are at risk for acquiring and transmitting hepatitis B, measles, and influenza; hence, vaccination against these diseases is recommended.